Manufacture of subminiature incandescent lamps

ABSTRACT

In the manufacture of a single ended subminiature incandescent lamp, helically coiled filament wire, while still on the mandrel wire on which it has been coiled, is unreeled from a spool and a predetermined length thereof is attached to the ends of a U shaped support wire. The filament is then inserted into acid to dissolve the mandrel and is subsequently sealed within a glass envelope. Each leg of the U shaped support is then converted into a lead-in wire by severing the midportion of the support.

United States Patent [191 Kimball et al. A

[ MANUFACTURE OF SUBMINIATURE INCANDESCENT LAMPS [75] Inventors: StephenF. Kimball, Georgetown;

Paul E. Gates, Danvers, both of Mass.

[73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

[22] Filed: June 7, 1973 [21] Appl. No.: 367,807

[52] [1.8. Cl. 29/25.15, 313/271 [51] Int. Cl. H01] 9/18 [58] Field ofSearch 29/2514, 25.15, 25.17, 29/2518, 25.1, 25.11, 25.13., 423; 313/3l5,271

. [56] References Cited UNITED STATES PATENTS 2,067,746 1/1937 Zabel29/.25.l3 X

111 3,863,313 Feb. 4, 1975 12/1967 Decker et al. 313/212 PrimaryExaminer-Roy Lake Assistant Examiner-James W. Davie Attorney, Agent, 0rFirmJames Theodosopoulos [57] ABSTRACT In the manufacture of a singleended subminiature' incandescent lamp, helically coiled filament wire,while still on the mandrel wire on which it has been coiled, is unreeledfrom a spool and a predetermined length thereof is attached to the endsof a U shaped supportwire. The filament is then inserted into acid todissolve the mandrel and is subsequently sealed within a glass envelope.Each leg of the U shaped support is then converted into a lead-in wireby severing the midportion of the support,

1 Claim, 4 Drawing Figures I MANUFACTURE OF SUBMINIATURE INCANDESCENTLAMPS BACKGROUND OF THE INVENTION This invention relates to single endedsubminiature lamps the illumination from which results from a tungstenfilament heated to incandescence by flow of electric currenttherethrough. lt especially relates to a method of making such lamps.

Subminiature lamps generally have a filament made of such fine wire thatit can only be seen' andhandled under magnification; thus the coil mountand assembly is done by hand with consequent high costs. The filament isgenerally made by helically coiling fine tungsten wire on a metalmandrel wire, several times its di-- ameter, in a long continuouslength. The coiling is heat treated to set it andis then cut intopredetermined fila-- ment lengths. The mandrel is dissolved in acideitherbefore or after the cutting step. The filament is then handmounted on a' suitable supportan'dthen sealed within a smallglass'envelope.

It is an object of this invention to provide a method of manufacturingthat permits employment of automatic assembly machines, therebyeliminating much'of the hand work involved and thereby significantlyreducing the cost of such lamp.

THE lNVENTlON In the drawing, v 1 FIG. 1 is an illustration of amandrel-containing, helically coiled lamp filament attached to the-endsof a U- shaped support wire.

FIG. 2 shows the supported filament immersed in acid to dissolve themandrel.

FIG. 3 shows the supported filament sealed in one end of a glass tubing.2

FIG. 4 shows the finished lamp.

In the manufacture of a single endedsubminiature incandescent lamp inaccordance with this invention,

fine tungsten wire 2, generally less'than 1 mil in diamea spool in along continuous length. Next, the coiling 2 is mounted on suitableapparatus where it can be continuously unreeled. The coiling is drawnacross the ends of a U shaped support wire 1 and a short length ofcoiling 2 is permanently connected to said ends, such as by welding orclamping, and cut. Said short length equals the distance between saidends and comprises the filament in the finished lamp. The fact that themandrel 7 is still within the coiling 2 gives it sufficient bulk topermit the unreeling and connecting steps'tobe performed on automaticequipment. The distance between legs of the U shaped support 1 is smallenough pletelydissolve the mandrel 7,' at least inthe case of a straightfilament, that is to say, acoiled filament where the mandrel isstraight. The support 1 need not be completely immersed as long as thefilament is. The acid 3 may be heated to reduce the time for dissolvingthe mandrel 7 to a few seconds/Typically,hydrochloric I acid is used todissolve a steelmandrel, while a combination of sulphuric and nitricacids is used to dissolve a molybdenum mandrel. Preferably, the support!is of a metal that is resistant to'the acid used.

After the filament is rinsed and dried, it is ready for sealing within aglass envelope 4. The filament end of the support 1 is inserted in oneend of a smalldiameter glass tubing-typically, T1 or inch diameter, andthe end of the tubing is heated to its softening point. The

softened end is then squeezed on part of the legs of the support to forma hermetic press seal 5. The support 1 is made of a wire, such as dumet,kovar or invar, that is sealable to glass; T

After the support 1 has been sealed in one end of the glass tubing, thetubing is exhausted through the other end and is thenheated and tippedoff to form the lamp envelope. 4. Thetubing at said other end may havepreviously been tubulated or necked down in diameter to aid in tippingoff the lamp;

The support 1 is then cut to remove the middle section of the U and eachleg of the support servesas a lead-in wire 6 for the filament. Ifdesired, the support 6, i.e., lead-in wire, may be of a material that isreadily solderable, to simplify final connection of the lamp.

In an example of a 5 volt 60 milliampere T1 lam'p made inaccordance-with this invention, the filament to permit it, with thefilament'connected therebetween,

coiling 2 consisted of 0.6- mil tungsten wire wound on 4 mil molybdenumwire 7 at 650 TPI'. The coiling was heat treated at 1,525TC and then 2mm lengths thereof were welded across the ends of U shaped supportwires 1. Each support 1 was made of 10 mil dumet wire, nickel plated,the distance between the ends of the U being 2 mm and the length: of thesupport being about l0 mm. The filament was then inserted into heatedsulfuric-nitric acid 3 for about S-to 10 seconds to dissolve themolybdenum mandrel 7 therein. After rinsing and drying, the filament 2,while still on the supportl, was inserted into one end of Tl glasstubing 4, open at both ends. The other end of the glass tubing 4 wasconnected, by a vacuum tight connection, to exhaust and fillingapparatus. The first end of the glass tubing 4 was heated to itssoftening point and then pressed onto part of the legs of the support 1to form a hermetic press seal 5. If necessary, the interior of thetubing could be flushed with a suitable inert gas to prevent oxidationof the filament during press sealing. The other end of the glass tubing4 was then. heated and tipped off while a vacuum was maintained inthetubing. The middle section of the support 1 was then removed by cutting,thereby forming two lead-in wires 6 for the filament.

The finished lamp had a diameter of about oneeighth inch and an overallenvelope length of about 6 mm. The lighted length of the filament wasabout 2 mm. The length of the press seal was about 2 /2 mm and thelength of the lead-in wires protruding outside the press was about 3 mm.The lamp was energized by suitable connection of said legs to a 5 voltpower supply.

. 3 the coiling-with-mandrel at the time it is drawn across the ends ofthe U support and is attached thereto. Or else the legs-of the U'may beexcessively open at the time of attaching the coiling-with-mandrelthereto; then partially closing said legs wouldresult in a somewhat Vshaped filament. In the case of a Vvfilament, it

1. In the process of manufacturing a single ended subminiatureincandescent lamp, the steps which sequentially comprise: helicallycoiling a length of fine tungsten wire on a mandrel wire having a largerdiameter; heat treating the coiling; connecting a predetermined lengthof the coiling across the ends of a U v shaped support wire, saidpredetermined length comprising a lamp filament; immersing said filamentinto acid to dissolve the mandrel therein; inserting the filament intoan open ended glass tube; heating and press sealing one end of the glasstube onto a portion of the legs of the support; sealing the other end ofthe glass tube; and removingthe middle section of the support so thateach leg thereof comprises a lead-in wire for the filament.

1. In the process of manufacturing a single ended subminiatureincandescent lamp, the steps which sequentially comprise: helicallycoiling a length of fine tungsten wire on a mandrel wire having a largerdiameter; heat treating the coiling; connecting a predetermined lengthof the coiling across the ends of a U shaped support wire, saidpredetermined length comprising a lamp filament; immersing said filamentinto acid to dissolve the mandrel therein; inserting the filament intoan open ended glass tube; heating and press sealing one end of the glasstube onto a portion of the legs of the support; sealing the other end ofthe glass tube; and removing the middle section of the support so thateach leg thereof comprises a lead-in wire for the filament.